1. Field of the Invention
This invention pertains to telecommunications, and particularly to the structure and operation of shared telecommunication networks.
2. Related Art and Other Considerations
In a typical cellular radio system, mobile user equipment units (UEs) communicate via a radio access network (RAN) to one or more core networks. The user equipment units (UEs) can be mobile stations such as mobile telephones (“cellular” telephones) and laptops with mobile termination, and thus can be, for example, portable, pocket, hand-held, computer-included, or car-mounted mobile devices which communicate voice and/or data with radio access network.
The radio access network (RAN) covers a geographical area which is divided into cell areas, with each cell area being served by a base station. A cell is a geographical area where radio coverage is provided by the radio base station equipment at a base station site. Each cell is identified by a unique identity, which is broadcast in the cell. The base stations communicate over the air interface (e.g., radio frequencies) with the user equipment units (UE) within range of the base stations. In the radio access network, several base stations are typically connected (e.g., by landlines or microwave) to a radio network controller (RNC). The radio network controller, also sometimes termed a base station controller (BSC), supervises and coordinates various activities of the plural base stations connected thereto. The radio network controllers are typically connected to one or more core networks.
One example of a radio access network is the Universal Mobile Telecommunications (UMTS) Terrestrial Radio Access Network (UTRAN). The UMTS is a third generation system which in some respects builds upon the radio access technology known as Global System for Mobile communications (GSM) developed in Europe. UTRAN is essentially a radio access network providing wideband code division multiple access (WCDMA) to user equipment units (UEs). The Third Generation Partnership Project (3GPP) has undertaken to evolve further the UTRAN and GSM-based radio access network technologies.
As those skilled in the art appreciate, in W-CDMA technology a common frequency band allows simultaneous communication between a user equipment unit (UE) and plural base stations. Signals occupying the common frequency band are discriminated at the receiving station through spread spectrum CDMA waveform properties based on the use of a high speed, pseudo-noise (PN) code. These high speed PN codes are used to modulate signals transmitted from the base stations and the user equipment units (UEs). Transmitter stations using different PN codes (or a PN code offset in time) produce signals that can be separately demodulated at a receiving station. The high speed PN modulation also allows the receiving station to advantageously generate a received signal from a single transmitting station by combining several distinct propagation paths of the transmitted signal. In CDMA, therefore, a user equipment unit (UE) need not switch frequency when handoff of a connection is made from one cell to another. As a result, a destination cell can support a connection to a user equipment unit (UE) at the same time the origination cell continues to service the connection. Since the user equipment unit (UE) is always communicating through at least one cell during handover, there is no disruption to the call. Hence, the term “soft handover.” In contrast to hard handover, soft handover is a “make-before-break” switching operation.
The Universal Mobile Telecommunications (UMTS) Terrestrial Radio Access Network (UTRAN) accommodates both circuit switched and packet switched connections. In this regard, in UTRAN the circuit switched connections involve a radio network controller (RNC) communicating with a mobile switching center (MSC), which in turn is connected to a connection-oriented, external core network, which may be (for example) the Public Switched Telephone Network (PSTN) and/or the Integrated Services Digital Network (ISDN). On the other hand, in UTRAN the packet switched connections involve the radio network controller communicating with a Serving GPRS Support Node (SGSN) which in turn is connected through a backbone network and a Gateway GPRS support node (GGSN) to packet-switched networks (e.g., the Internet, X.25 external networks). MSCs and GSNs are in contact with a Home Location Register (HRL), which is a database of subscriber information.
There are several interfaces of interest in the UTRAN. The interface between the radio network controllers (RNCs) and the core network(s) is termed the “Iu” interface. The interface between a radio network controller (RNC) and its base stations (BSs) is termed the “Iub” interface. The interface between the user equipment unit (UE) and the base stations is known as the “air interface” or the “radio interface” or “Uu interface”. In some instances, a connection involves both a Serving or Source RNC (SRNC) and a target or drift RNC (DRNC), with the SRNC controlling the connection but with one or more diversity legs of the connection being handling by the DRNC. An Inter-RNC transport link can be utilized for the transport of control and data signals between Source RNC and a Drift or Target RNC, and can be either a direct link or a logical link as described, for example, in International Application Number PCT/US94/12419 (International Publication Number WO 95/15665). An interface between radio network controllers (e.g., between a Serving RNC [SRNC] and a Drift RNC [DRNC]) is termed the “Iur” interface.
The radio network controller (RNC) controls the UTRAN. In fulfilling its control role, the RNC manages resources of the UTRAN. Such resources managed by the RNC include (among others) the downlink (DL) power transmitted by the base stations; the uplink (UL) interference perceived by the base stations; and the hardware situated at the base stations.
Those skilled in the art appreciate that, with respect to a certain RAN-UE connection, an RNC can either have the role of a serving RNC (SRNC) or the role of a drift RNC (DRNC). If an RNC is a serving RNC (SRNC), the RNC is in charge of the connection with the user equipment unit (UE), e.g., it has full control of the connection within the radio access network (RAN). A serving RNC (SRNC) is connected to the core network. On the other hand, if an RNC is a drift RNC (DRNC), its supports the serving RNC (SRNC) by supplying radio resources (within the cells controlled by the drift RNC (DRNC)) needed for a connection with the user equipment unit (UE). A system which includes the drift radio network controller (DRNC) and the base stations controlled over the Iub Interface by the drift radio network controller (DRNC) is herein referenced as a DRNC subsystem or DRNS. An RNC is said to be the Controlling RNC (CRNC) for the base stations connected to it by an Iub interface. This CRNC role is not UE specific. The CRNC is, among other things, responsible for handling radio resource management for the cells in the base stations connected to it by the Iub interface.
The UTRAN interfaces (Iu, Iur and Iub) have two planes, namely, a control plane (CP) and a user plane (UP). In order to control the UTRAN, the radio network application in the different nodes communicate by using the control plane protocols. The RANAP is a control plane protocol for the Iu interface; the RNSAP is a control plane protocol for the Iur interface; and NBAP is a control plane protocol for the Iub interface. The control plane protocols are transported over reliable signaling bearers. The transport of data received/transmitted on the radio interface occurs in the user plane (UP). In the user plane, the data is transported over unreliable transport bearers. The serving radio network controller (SRNC) is responsible for establishing the necessary transport bearers between the serving radio network controller (SRNC) and the drift radio network controller (DRNC).
It has recently been contemplated that two or more operators can share network infrastructure, e.g., share a UTRAN in a particular geographical area. In the shared network all of the UTRAN resources are shared, e.g. RNCs, node-Bs, cells, etc, and can be used equally by subscribers of both sharing operators. Using shared networks, operators can reduce the cost of network build-out.
When user equipment units are leaving the coverage area of the shared network (e.g., leaving a shared network cell), it is likely that each operator will require that their own subscribers handover to their own home network. If, however, cells from both operators home networks neighbor the shared network cell, a problem of possibly handing over the user equipment unit to the wrong network when leaving the shared network coverage area must be addressed.
This problem can be solved by a technique which includes filtering out the cells that are not possible/permitted (or not preferred) for handover for a given user equipment unit, and only sending the list of allowed neighbor cells to the user equipment unit, so that the user equipment unit can measure on those cells, and send the results to the RNC. The RNC will then choose a cell to which to handover to based on the measured results. This technique will herein be called “selective handover”.
The cell filtering is performed based on the international mobile subscriber identity (IMSI) of the user equipment unit. The international mobile subscriber identity (IMSI) is stored in the RNC for each connected mode user equipment unit. The international mobile subscriber identity (IMSI) is received in the RNC from the core network (CN) in a RANAP COMMON ID message when a radio resource control (RRC) connection is setup. The international mobile subscriber identity (IMSI) [which comprises not more than fifteen digits] comprises three components: a mobile country code (MCC)[three digits]; a mobile network code (MNC)[two or three digits]; and a mobile subscriber identification number (MSIN). The home-public land mobile network (HPLMN) id [HPLMNid] of the user equipment unit can be extracted from the international mobile subscriber identity (IMSI). In this regard, the HPLMNid of the user equipment unit is the mobile country code (MCC)+the mobile network code (MNC). The HPLMN id can be compared against a filtering rule for a given neighbor cell in order to check whether the user equipment unit should be allowed to handover to that cell.
The filtering rule can be as simple as comparing the PLMNid of the neighbor cell itself to the HPLMNid of the user equipment unit. If they are the same, only cells from the current PLMN, and from the PLMN equal to the HPLMN of the user equipment unit, are included in the measurement list sent to the user equipment unit.
The “measurement list” is the list of cells that the system (e.g., network) sends the user equipment unit, in order that the user equipment unit should perform measurements (e.g., signal strength measurements) for these cells. The measurement list includes both cells in the active set and cells in the monitored set. The “active set” is comprised of cells involved in soft/softer handover (macro diversity) for which the UTRAN requires the UE to perform measurements (the active set is defined in 3GPP). The “monitored set” comprises cells, which although not included in the active set, are required by the UTRAN for the user equipment unit to perform measurements, i.e., cells in the neighbor set that the user equipment unit is required to measure on (Defined in 3GPP). The “neighbor set” is the union of the neighbor cells of the cells in the active set with exclusion of the cells in the active set. The “listed set” is the sum of the active set and the monitored set, i.e., all cells that UTRAN requires the user equipment unit to measure on. The “detected Set” comprises cells that the user equipment unit can detect, that are included neither in the active set or the monitored set.
The user equipment unit reports to the SRNC the signal strength for the cells included in the measurement list. The SRNC analyzes the reported measurements and may perform a handover for cells whose signal strength measurements satisfy criteria of the SRNC. Performing a handover in this context may involve, e.g., setting up a radio link or connection leg in a diversity situation, i.e., adding a new radio link to the active set for the user equipment unit.
The selective handover function can also be required in other cases, for example in the geographical split solution to shared networks, where the operators cover different areas of a country, but allow other operators to use their network through roaming agreements. In some cases the geographically split networks will overlap in coverage, and again each operator will require their own subscribers to return to their own home network. In this regard, see (for example) U.S. Patent Application Ser. No. 60/301,442, filed Jun. 29, 2001, entitled “Partial Support of Mobility Between Radio Access Networks”, which is incorporated herein by reference in its entirety.
The filtering for selective handover is best performed in the serving radio network controller (SRNC) where the radio resource control (RRC) connection for a user equipment unit is terminated, and where the measurement list of the user equipment unit is handled. However, unfortunately the serving radio network controller (SRNC) only knows the filtering rules (for example which PLMNs are allowed, and which are not) for cells in the SRNC (e.g., cells controlled by the SRNC), and those cells in the DRNC that the SRNC has configured as external cells. When a user equipment unit hands over from a cell in an SRNC to a target cell controlled by a DRNC, the SRNC receives information on neighboring cells adjacent the new DRNC cell (i.e., the new target cell) from the DRNC. Some of these neighboring cells may be defined already as neighbor cells in the SRNC, but quite possibly some will not already be so defined, as they may be “neighbors” to the neighbor cells already defined in the SRNC.
At this juncture of having completed the handover to the target cell, the SRNC would like to send a filtered measurement list to the UE over the RRC connection, telling the UE which cells to measure handover criteria on (e.g., signal strength or some other criteria). Desirably the filtered list would include whichever of the new neighbor cells received from the DRNC are permitted for the user equipment unit. However the SRNC does not know the filtering rules for the DRNC neighbor cells.
What is needed, therefore, and an object of the present invention, is a technique to facilitate filtering of cells for use in a measurement list in conjunction with a selective handover situation from a shared network.